Ancient sediments from Greenland

Ancient sediments from Greenland

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The oldest-known sedimentary rocks on the Earth comprise the 3.8-billion-year-old Isua Sequence of southwestern Greenland. The rocks were once sediments formed by chemical precipitation from ocean water. Intermittent eruptions from nearby volcanoes added other sediment layers. The Isua rocks tell geologists important things about the early Earth: (1) there already was an ocean in which the sedimentary laters were laid down; (2) volcanoes already existed; and (3) erosion of the rocks was promoted by an atmosphere rich in carbon dioxide and water vapor. The rocks also contain geochemical evidence of the earliest life.